1. Field of the Invention
This invention is directed to a method and apparatus for making a cutting tool having at least one helical flute and land and having a margin on the land. In particular, the invention is directed to a single grinding wheel and method of using such a grinding wheel to produce both the flute and land portions of the cutting tool, including a margin associated with the land.
This invention is also directed to a crush roll used to form such a grinding wheel.
2. Description of Related Art
A cutting tool, such as a twist drill, is generally comprised of a cylindrical shaft having at least one flute and land, wherein the flute and the land follow a helical angle to a forward cutting edge of the forward end of the shaft. The flute has associated with it a lip and an adjacent nose. The land has associated with it a clearance portion and a margin adjacent to the clearance portion. A side cutting edge is defined by the intersection of the lip with the margin of the land. Associated with the land of the cutting tool may be a single margin or, in some instances, a double margin wherein one margin is on each side of the land. In the past, production of such a cutting tool having both a helical flute and land with a margin required two separate grinding operations. In one operation, the flute would be ground with one grinding wheel, and in a separate operation the land would be ground with a second grinding wheel.
These two separate grinding operations require mounting the cutting tool on two separate grinding machines. Therefore, the cutting tool must be precisely mounted within each grinding machine to ensure the flute and land are ground along the same helical path. Additionally, the grinding machines must be set at the same lead angle to ensure the flute and land are ground along the same helix angle. If the cutting tool is not properly mounted and the flute and land are not ground correctly, the tool may be flawed such that it must be discarded. Furthermore, setup for two separate operations is not only time-consuming but also prone to error. Therefore, while the cutting tool could be ground using two grinding operations, a single grinding operation would be preferred.
A need exists to eliminate the need for two separate grinding operations to produce a drill having a margin through the use of a single grinding wheel and a method for using the same.
Finally, such a grinding wheel may be produced using single point dressing tools or CNC machines. However, each of these methods is time-consuming and expensive. As a result, a method and apparatus is desired for producing such a grinding wheel in a more efficient manner.
The invention is directed to a grinding wheel for producing a helical cutting tool having a shaft with a longitudinal axis, wherein the cutting tool shaft has a forward end and, when viewed in cross-section perpendicular to the longitudinal axis and spaced from the forward end, the cutting tool is comprised of a flute having a radial depth and a land adjacent to the flute wherein the flute and the land extend about the longitudinal axis of the shaft along a helix angle. The flute has a lip extending inwardly from an outer radius and a nose adjacent to the lip. Each land has a clearance portion adjacent to the nose and a margin adjacent to the clearance portion. The grinding wheel is comprised of a disk having a disk centerline and an average radial size, a first side and a second side defining a width therebetween and a disk outer edge between the sides, wherein the outer edge has an abrasive material for grinding a cutting tool. The edge has a profile defined by:
a) a lip shaper segment extending in a lateral direction from the first side and extending away from the disk centerline a radial distance defining the radial depth of the flute;
b) a nose shaper segment adjacent to the lip shaper segment and extending in a lateral direction toward the second side and extending inwardly toward the disk centerline;
c) a clearance shaper segment adjacent to the nose shaper segment and extending in a lateral direction toward the second side; and
d) a margin relief shaper segment adjacent to the clearance shaper segment and extending in lateral direction toward the second side and extending toward the disk centerline.
Another aspect of the invention is directed to a method of producing a helical cutting tool having a shaft with a longitudinal axis, wherein the cutting tool shaft has a forward end and, when viewed in cross-section perpendicular to the longitudinal axis and spaced from the forward end, has a flute with a radial depth and has a land adjacent to the flute. The flute and the land extend about the longitudinal axis of the shaft along a helix angle. The flute has a lip extending inwardly from an outer radius and a nose adjacent to the lip and wherein each land has a clearance portion adjacent to the nose and a margin adjacent to the clearance portion. The method comprises the step of:
a) producing both the flute and land of the cutting tool by grinding the shaft with at least one pass of a grinding wheel.
Yet another aspect of the invention is directed to a cutting tool having a shaft with a longitudinal axis and a forward end and, when viewed in cross-section perpendicular to the longitudinal axis and spaced from the forward end, the cutting tool is comprised of a flute having a radial depth and a land adjacent to the flute. The flute and land extend about the longitudinal axis of the shaft along a helix angle. The flute has a lip extending inwardly from an outer radius and a nose adjacent to the lip and wherein each land has a clearance portion adjacent to the nose and a margin adjacent to the clearance portion, wherein the cutting tool is produced with a method comprising the step of:
a) producing both the flute and land of the cutting tool by grinding the shaft with at least one pass of a single grinding wheel.
Yet another aspect of the invention is directed to a crush roll for dressing a grinding wheel, wherein the grinding wheel is used to produce a helical cutting tool having a shaft with a longitudinal axis. The cutting tool shaft has a forward end and, when viewed in cross-section perpendicular to the longitudinal axis and spaced from the forward end, is comprised of a flute having a radial depth and a land adjacent to the flute. The flute and the land extend about the longitudinal axis of the shaft along a helix angle. The flute has a lip extending inwardly from an outer radius and a nose adjacent to the lip and wherein each land has a clearance portion adjacent to the nose and a margin adjacent to the clearance portion. The crush roll is comprised of a disk having a disk centerline and an average radial size, a first side and a second side defining a width therebetween and a disk outer edge between the sides, wherein the sides and edge have an abrasive material for dressing the grinding wheel. The edge has a profile defined by:
a) a lip former segment extending in a lateral direction from the first side and extending toward the disk centerline a radial distance defining the radial depth of the flute;
b) a nose former segment adjacent to the lip shaper segment and extending in a lateral direction toward the second side and extending outwardly away from the disk centerline;
c) a clearance former segment adjacent to the nose former segment and extending in a lateral direction toward the second side; and
d) a margin relief former segment adjacent to the clearance former segment and extending in a lateral direction toward the second side and extending away from the disk centerline.